In a manner that is full of color, vivid, or interesting; described with bright or varied colors, or expressed in a lively and expressive way.
From 'colorful' (adjective) plus '-ly' (adverb suffix), following standard English derivation. The adjective 'colorful' emerged in the 19th century.
When people say someone speaks 'colorfully,' they often mean they use vivid, creative language—sometimes including colorful language (as a polite way of saying swearing), because colors and vibrance have been metaphors for intensity and liveliness in English for centuries.
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